The present invention relates to a slip controlled brake system comprising a pedal-actuated, auxiliary pressure supported braking pressure generator to which the wheel brakes are connected by way of pressure medium conduits, and of a hydraulic auxiliary pressure supply system comprising a hydraulic pump, a pressure compensating and pressure medium supply reservoir, and an auxiliary pressure control valve. The system is provided with wheel sensors as well as electronic circuits for determination of the rotational behavior of the wheels and for generation of electric braking pressure control signals permitting control of electromagnetically actuatable pressure inlet and outlet valves inserted in the pressure medium conduits for slip control.
In known brake systems of this type (DE-OS 30 40 561, DE-OS 30 40 562), a master cylinder with a hydraulic brake force booster connected upstream of it is used as a braking pressure generator. The auxiliary pressure supply system comprises a hydraulic pump and a hydraulic accumulator from which, in application of the brake, an auxiliary pressure proportional to the pedal force is derived by means of a control valve. This dynamic pressure, on the one hand, is transmitted by way of the master cylinder to the static brake circuits connected to the master cylinder. On the other hand, the pressure chamber into which the pressure proportional to the pedal force is introduced is directly connected with the wheel brakes of one axle, preferably the rear axle. Further more, inlet valves are inserted in both the static circuits and the dynamic circuit for slip control, the inlet valves being normally open and permitting, in case of imminent blocking of a wheel, to interrupt the inflow of pressure medium to the respective wheel. In addition, there are outlet valves through which pressure medium can be drained, if necessary, towards the pressure compensating reservoir. As the slip control action starts, the booster chamber, in which the controlled pressure fed in from the auxiliary pressure supply system prevails, is connected by way of a so-called main valve with the static brake circuit of the master cylinder, in order to allow the volume of pressure medium drained off by way of the outlet valves to be reintroduced into the static circuits. Furthermore, the piston (or pistons) in the (tandem) master cylinder are turned or stopped, for safety reasons, by means of a positioning device. The construction expediture required for generating, accumulating, and controlling the hydraulic auxiliary pressure, for dynamic inflow into the static circuits, and for assuring the brake functions in case of failure of individual circuits is considerable.
In brake systems of this type, the signals for control of the inlet and outlet valves are generated by means of electronic circuits of which the inputs are connected with wheel sensors (e.g., inductive sensors) and are thus able to react to any change of the rotational behavior of the wheels indicating a blocking danger by maintaining, decreasing, and re-increasing the pressure at the respective wheel.
The object of the present invention, therefore, is to overcome the described disadvantages of the known slip-controlled brake systems and to develop a slip-controlled brake system which can be produced at comparatively low expense with out any loss in terms of functionability.